Looking at the coils you should get a clearer picture of how the coils function. The more the number of coils in it the more wattage you'll need, the liquid consumption will be more and the vapor production will also be more. But seeing that currently you're a little uncomfortable with the 0.4 at 30w i wouldn't recommend t8 for now. The rest you should get comfortable with in some time when you've vaped for a couple of weeks.